The present invention relates to a latch device, and more particularly to a device for latching an airplane landing gear or an airplane landing gear hatch.
In a conventional approach, latch devices of this type comprise a box containing a set of hinged elements mounted to pivot about respective parallel axes, said assembly including at least a hook and a locking lever connected to said hook by associated elastically deformable return means. The hook can then be unlocked by acting on the locking lever either via first actuator means in a normal mode of operation, or via a second actuator means in an emergency mode of operation in the event of said first actuator means not managing to unlock the hook.
The main problem the invention seeks to solve relates to the structure and the arrangement of the second actuator means which is associated with the emergency mode of operation.
This second actuator means is used in an emergency mode of operation when the first actuator means fails to unlock the hook. This is a breakdown situation, in which the landing gear fails to be extended normally. The weight of the landing gear then acts as a large load on the hook. Consequently, in order to manage nevertheless to unlock the hook, it is necessary to develop a high level of torque in order to overcome any ceasing of the moving part.
Conventionally, the second actuator means associated with emergency mode operation is constituted by an electromechanical actuator implemented in the form of a common electric motor which controls both the rodding of the latch boxes of the airplane and the associated hydraulic valves. This requires the presence of a linkage that is relatively heavy and that is always difficult to adjust during maintenance. The manufacturer must ensure specific sequencing in an emergency situation: the hydraulics are initially switched off, then the hydraulics are connected to the return circuit; after which the hatch latches are released, and finally the landing gear latches are released.
The closest state of the art is illustrated by document U.S. Pat. No. 5,288,037 in the name of the Applicant.
That document describes a latching box of the type comprising a hinged locking lever having a first branch that carries a bearing wheel co-operating with a cam surface of a hook, and having a second branch that is connected, by means of a linkage, to the outlet shaft of a motor and stepdown gear box unit. For emergency unlocking, an oblong slot is provided in the linkage so as to enable the hook to pivot in spite of being locked, and an independent actuator sufficient to pivot the unlocking lever and disengage the bearing wheel. The independent actuator is, however, made in the form of a single-use pyrotechnic actuator (triggering by a powder cartridge which releases a propeller gas).
It should be observed that such a pyrotechnic actuator cannot be compared to an independently electrically controlled electromechanical actuator.
The technological background is also illustrated by documents DE-C-731 274, U.S. Pat. No. 3,504,406, and EP-A-0 265 197.
It would thus be advantageous to design a latch device in which the second actuator means associated with the emergency mode of operation is capable of developing high torque in order to be able to unlock the hook while it is loaded, but without that making it necessary to overdimension the motors or to accept the constraints of a heavy linkage.
As a subsidiary point, another problem relates to the first actuator means which acts in a normal mode of operation.
The first actuator means is generally made in the form of a linear actuator of the hydraulic type. The advantage of such actuators is that they are reliable in operation since the technology has been mastered for a long time. Reference can be made to document GB-A-2 161 202.
That document describes a bolt which, in normal circumstances, secures the parts forming the hook. Action on the rod enables said connection to be unlocked in the event of blockage, and to be rotated relative to said parts. The actuating means associated with normal operation is a conventional linear actuator of hydraulic type (actuator 28).
At the end of the description, it is briefly indicated that electrically controlled actuating means can be used as a variant, but the text does not mention the power and the independent characteristic of said possible electrical control.
Nevertheless, the present trend is more and more towards limiting the use of hydraulic components because of their large weight and also because of the risk of leakage associated therewith.
In addition, with the hydraulic arrangement that is conventionally used, a single feed block is provided directing fluid both to the actuator for driving the landing gear and to the latch block. Thus, when it is desired to unlock the hook, the hydraulic control acts simultaneously on the drive actuator, thereby tending to further increase the load exerted on the hook, and consequently to make it necessary to use a latch device capable of developing a force that is sufficiently large to be capable of overcoming the load forces exerted on the hook and to be capable of absorbing the internal energy generated by opening the hook while under said loading. Naturally, the amount of power required means that it is necessary to provide elements that are of non-negligible weight, and that is always unfavorable in the field of aviation.
It thus appears to be advantageous to be capable of providing a latch device which is fitted with first actuator means associated with a normal mode of operation that are capable of achieving unlocking while developing a minimum amount of power, with unlocking also taking place in normal mode without generating noise or vibration, while nevertheless withstanding the high levels of heating that can be encountered.
According to the invention, the main problem specified above is solved by a latch device, in particular for latching an airplane landing gear or an airplane landing gear hatch, the device comprising a box containing a set of hinged elements mounted to pivot about respective parallel axes, said assembly including at least one hook and a locking lever connected to said hook by associated elastically deformable return means, said hook being capable of being unlocked by acting on said locking lever either via first actuator means in a normal mode of operation, or via a second actuator means in an emergency mode of operation when said first actuator means fails to unlock the hook, the second actuator means associated with the emergency mode of operation being an electromechanical actuator under independent electrical control, said actuator comprising two electric motors associated in irreversible manner with a common differential gear train, having an outlet shaft controlling the pivoting of an emergency unlocking lever co-operating with the locking lever used in normal operation.
Advantageously, each motor of the electromechanical actuator is fitted downstream with a torque limiter, preferably of the magnetic type, and each motor is also fitted at its outlet with irreversible clamping means, e.g. of the magnetic, mechanical, or friction type.
In a first embodiment, the outlet shaft of each of the two motors engages an associated stepdown gear train, the respective outlet shaft thereof being coupled in irreversible manner to the common differential gear train, the outlet shaft of the common differential gear train causing the emergency unlocking lever to pivot. In particular, each stepdown gear train comprises spur gears, and the irreversible connection of its outlet shaft to the common differential gear train which is likewise made of spur gears, is provided by means of an associated wormscrew.
In another embodiment, the outlet shaft of each of the two motors is coupled in irreversible manner to the common differential gear train, and the outlet shaft of said common differential gear train is connected to the inlet of an epicyclic stepdown gear train, the outlet shaft of said epicyclic stepdown gear train causing the emergency unlocking lever to pivot. In particular, the irreversible connection of each outlet shaft with the common differential gear train which is made up of spur gears is provided by means of an associated wormscrew.
In yet another embodiment, the outlet shaft of each of the two motors is connected to a common differential gear train made of bevel gears via an associated non-return mechanism, and the outlet shaft of said common differential gear train is connected via a torque limiter to a stepdown gear train whose outlet shaft causes the emergency unlocking lever to pivot. In particular, the torque limiter is a friction torque limiter, and the stepdown gear train is made of spur gears.
Also preferably, the electromechanical actuator with its two electric motors and its common differential gear train is fixed to the box in removable manner, and is easily accessible, thereby enabling it to be directly replaced by another actuator without needing to dismantle said box.
Finally, and advantageously, the first actuator means associated with the normal mode of operation is likewise an electromechanical actuator under independent electric control, said actuator being of low power and being constituted by an electromagnet, or a motor and stepdown gear box unit, or a torque motor of small size.
Other characteristics and advantages of the invention appear more clearly in the light of the following description and the accompanying drawings, relating to a particular embodiment.